1. Technical Field
This invention relates generally to telecommunications, and more particularly, to a method for restoring internal path and equipment failures in a hybrid broadband access-and-transport network system.
2. Related Art
Two closely interrelated segments of multi-service networking are “access” and “transport.” “Access” refers to the technology by which users connect to a wide area network (“WAN”), and through it, to service providers or other users connected to the WAN at locations remote from the user. “Transport” refers to the technologies that make up the fabric of the WAN itself, including those relating to the transmission of the users' information across the WAN.
One model of a high-speed access-and-transport network system for which detailed standards have been developed by the International Telecommunication Union (“ITU”) is the “Broadband Integrated Services Digital Network” (“BISDN”) “umbrella” model, which, in one widely regarded embodiment, can be characterized as Asynchronous Transport Mode (“ATM”) over a Synchronous Optical Network (“SONET”) transmission system (“ATM/SONET”).
Thus, one conventional paradigm of a BISDN access-and-transport system contemplates, 1) the “gathering” of lower-level voice, video, and data signals in a variety of formats from a large number of individual users at a “user network interface” (“UNI”) located at the edge of a WAN, 2) the “grooming” of those signals, first by “ATM-izing,” or “cellification” of the signals, if necessary, into fixed-length ATM cells, then by packaging, or “mapping,” the ATM cells into SONET synchronous payload envelope (“SPE”) structures, or “Synchronous Transport Stream” (“STS”) frames, of incremental capacities using high-speed switching techniques and an addressing system of “pointers” and transport and path overhead (“TOH” and “POH”), and 3) the “scattering” of the signals out over the WAN to their intended destinations.
However, some concerns exist regarding the “ATM/SONET” paradigm as it pertains to certain types of traffic, viz., voice and video signals, which are inherently isochronous or plesiochronous (i.e., time-division-multiplexed (“TDM”) traffic), as well as Internet Protocol (“IP”) traffic, which, unlike both ATM and TDM traffic, is by nature “connectionless.” While it is possible to ATM-ize both types of traffic, the resultant loss of bandwidth can greatly offset the increase in effective bandwidth afforded by the “statistical multiplexing” capabilities of ATM.
In light of the foregoing concerns, the assignee hereof has developed a novel, multi-functional, “hybrid” access-and-transport system, called the “C7” system, that is capable of supporting a wide variety of user interfaces, in terms of bandwidth, density, interface and application. It is a “hybrid” system, in that it is capable of efficiently gathering, grooming, and transporting both classical time division multiplexed (“TDM”) and packet-switched (i.e., ATM, Multiprotocol Label Switching (“MPLS”), IP, Packet Over SONET (“POS”), and Frame Relay) types of traffic streams in their respective formats and protocols, thereby maximizing available bandwidth through the use of statistical multiplexing, while preserving or even improving the QoS level achievable in such a disparate traffic mix. The C7 system can be deployed in any of several different topologies, including linear point-to-point, ring, star, mesh or any combination of the foregoing.
As those of skill in the art will appreciate, it is necessary for economic reasons to provide “end-to-end” protection for the traffic carried within any broadband access and transport system, i.e., some method for quickly “healing,” or restoring, the flow of traffic in the system in the event of an equipment failure or other problem in the transport media, such as a break in a fiber.
In the C7 system, a “concatenated” form of end-to-end traffic protection is provided that comprises two parts: 1) An “external” form of “equipment protection” applied between the users and the access “nodes” at the edge of the system, which is described in the above-referenced patent application Ser. No. 09/793,071, filed Feb. 26, 2001, and 2) an “internal” form of traffic protection described herein as an “Optical Mesh Restoration Protocol” (“OMRP”), that is applied to the internal core of the network.
Conventional “pure TDM” network equipments can implement either a line protection method, or a Virtual Tributary/STS (“VT/STS”) path protection method. Examples of such methods and equipments may be found in, e.g. U.S. Pat. No. 5,757,774 to Oka; U.S. Pat. No. 5,572,513 to Yamamoto et al.; U.S. Pat. No. 5,307,353 to Yamashita et al.; and U.S. Pat. No. 5,003,531 to Farinholt et al. However, “pure packet” (e.g. ATM, MPLS, or IP) based equipments implementing such a VT/STS path protection method cannot take advantage of the statistical multiplexing ability afforded by packet technology without the use of some form of external grooming equipment, e.g., ATM switches, IP routers, IP switches, and MPLS switches.
Conventional “pure ATM” equipments can implement either line protection or Virtual Path (“VP”) protection methods, but not both. A pure ATM system implementing path switching may be found in U.S. Pat. No. 5,150,356 to Tsutsui. However, existing VP path protection standards do not support so-called “self-healing” rings, nor do they support TDM traffic unless it is first ATM-ized, with the resultant significant loss in bandwidth problem described above.
Conventional ATM-over-SONET equipments can implement either VP path switching, at the path layer, or VT/STS line or path switching, at the transport layer, or both, in a complex, “multi-layered” approach. In such systems, it is necessary to apply some technique, such as a time delay mechanism, to one of the protection methods, typically the slower of the two, to prevent one method from interfering with the other. An example of such a multi-layered approach with a time delay mechanism in an ATM/SONET network can be found in U.S. Pat. No. 5,838,924 to Anderson et. al.
There are currently no standard IP traffic protection methods, other than the conventional IP packet “rerouting” algorithms, e.g. the “Open Shortest Path First” (“OSPF”) protocol.
A hybrid system, i.e., one that can support TDM, ATM and MPLS packets, e.g., MPLS IP packets, such as the C7 system, can implement either a line switching or a path switching protection method. However, while a line protection method is easier to implement in a hybrid system, a path protection method provides more overall protection coverage, and hence, is preferable to the former.
One possible path protection method for hybrid equipment is the conventional STS/VT path protection method. However, this method does not permit a hybrid equipment to take full advantage of the statistical multiplexing capabilities provided by packet technologies. A need therefore exists for a new path protection and restoration method for a hybrid equipment that takes full advantage of both the statistical multiplexing capability provided by packet (i.e., ATM, MPLS, IP) switching technology, as well as the “self-healing” properties of a ring topology, and yet one which can also support conventional TDM without requiring the TDM traffic to be packetized.